Fix DECCKM support for arrow keys in TUI apps (mc, vim, htop)

- mc/vim/htop enable Application Cursor Mode (DECCKM ?1h) which
  requires arrow keys to send \eOA..D instead of \e[A..D
- Detect DECCKM in pyte screen mode and send correct sequences
- Fix thread-safety: use queue.Queue for SSH→main thread data transfer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/widgets/terminal_widget.py

@@ -33,7 +33,10 @@ _DEFAULT_BG = "#1a1a2e"
 _CURSOR_FG = "#1a1a2e"
 _CURSOR_BG = "#d3d7cf"
 
-# Key → VT100 escape sequence
+# DECCKM (private mode ?1) — pyte stores private modes shifted by 5 bits
+_DECCKM = 32
+
+# Key → VT100 escape sequence (normal cursor mode)
 _KEY_MAP = {
     "Up":        "\x1b[A",
     "Down":      "\x1b[B",
@@ -59,6 +62,16 @@ _KEY_MAP = {
     "F12":       "\x1b[24~",
 }
 
+# Application cursor mode (DECCKM) — mc, htop, vim enable this
+_KEY_MAP_APP_CURSOR = {
+    "Up":    "\x1bOA",
+    "Down":  "\x1bOB",
+    "Right": "\x1bOC",
+    "Left":  "\x1bOD",
+    "Home":  "\x1bOH",
+    "End":   "\x1bOF",
+}
+
 
 class TerminalWidget(tk.Frame):
     """VT100 terminal emulator widget using pyte + tkinter.Text."""
@@ -301,9 +314,13 @@ class TerminalWidget(tk.Frame):
                 self._send(bytes([ord(ch) - ord("a") + 1]))
                 return "break"
 
-        # Special keys
+        # Special keys — check DECCKM (application cursor mode) for arrow keys
         if event.keysym in _KEY_MAP:
-            self._send(_KEY_MAP[event.keysym].encode())
+            decckm = _DECCKM in self._screen.mode
+            if decckm and event.keysym in _KEY_MAP_APP_CURSOR:
+                self._send(_KEY_MAP_APP_CURSOR[event.keysym].encode())
+            else:
+                self._send(_KEY_MAP[event.keysym].encode())
             return "break"
 
         # Tab